Dense papers and process for preparing them



United States Patent 7 i DENSE PAPERS AND PROCESS FOR PREPARINGJT HEM This invention relates to papers of high density and more particularly to high density glassine papers'of greatly ienhanced resistance to penetration of gases and greases and to a process for preparing them. I f

Glassine: paper has been produced in the past by first forming a highly hydrated chemical wood paper such as sulfite pulp paper, knownas greaseproof paper, then adding moisture to such paper to the extent of up to about 50%, usually between about 20% and about 30% of its total weight, and subjecting the moist sheet to supercalend'ering.

'The resulting glassine paper is a thin, translucent, dense paper having a considerable degree of grease and gas penetration resistance, and finds wide use in protecting food products, for example, in lining cereal and cracker cartons, in candy boxes, candy cups, etc., and has numerous other well established uses.

While the grease and gas resistance of conventionally prepared glassine papers is considerably higher than that of ordinary book or bond paper, such papers often contain imperfections such as thin spots or so-called pin holes which cause small areas. to be permeable to gas and grease in a sheet otherwise highly resistant to these "ice an aqueous emulsion of the oxidized polyethylene waxis applied to the paper by any convenient method of ap-' plication, adapted to apply the required amount of emul-* sion to the sheet and to assure its absorption into and onto the fibers of the sheet. If desired, an excess of emul-' sion may be, and usually is, applied, and this excess is removed by suitable treatment after' application such as passage through squeeze rolls or the like. The emulsion treated sheet may then be *wetcalendered" immediately, but preferably will be reeled after treatment with emul- @sion, wrapped in a moistureproof wrapping and held for a sufficient time to insure uniform penetration of the impregnating emulsion.

The treated. paper is then wet calendered on heated rolls in the manner customarily ,used in calendering to produce dense papers such as glassine paper, e.g., in a multi-roll super-calender stack, containing for example, from 9 to 20 rolls, usually of alternating chilled iron and compressed paper rolls, but which may have two or more adjacent paper rolls, and having their roll surfaces heated to between about 150 F. and about 270 F., depending factors, so thatadequatemeans for curing suchimperfec- The resulting papers have greatly increased densities as measured by specific gravity, usually being greater than 1, for example, at least about 1.05, often as high as- 1.2 or more. Density of papers is more often expressed in terms of porosity, for example, as measured by the Gurley densometer in which the results are reported in number of seconds required for 100 ml. of air to pass through one square inch of paper. When measured in this manner, the treated papers of my invention may have densities up to 10 times, i.e. 1,000% as great as those of the original untreated paper,and upto 4 times, i.e. 400% as great as finished papers, such as glassine, prepared from the same rawstock according to conventional procedures for preparing glassine papers for example about 30,000. This reduction in gas permeability greatly enhances the value of the papers for uses in protecting products from contact with air or other gases, for example, in food packaging and the like.

When greaseproof grade of paper has beenused as the rawstock, the resulting sheet is a dense glassine paper having the desirable properties of ordinary glassine plus used for coating papers are either soluble in, or softened by the commonly encountered oils.

It is an object of the present invention to provide high density papers, and a, process for preparing them.

Itis anotherobject of the invention to provide a glassine paper-of greatly enhanced grease resistance.

A further object is to provide a process for preparing a highly grease resistant glassine type paper which process can be carried out on the regular equipment commonly used in glassine production and with no additional process steps.

Astill furtherobject of my invention is to provide a process for treating glassine paper which not only greatly enhances its grease resistance, but which also improves its resistance to permeation by airand other vapors including water vapor.

Another, object is to provide a glassine paper of greatly enhanced density characteristics.

These and other objects are accomplished according to,

improved gloss and greatly enhanced density and grease resistance, the latter characteristic being partly a function of the density, partly a function of relative freedom from imperfections such as pin holes, etc. and depending to some extent on the oil or grease to which the paper is exposed. Thus, as compared to glassine papers finished by wet calendering alone without addition of oxidized polyethylene wax, the same papers treated in accordance with my invention may show grease resistance characteristics, for example, as much as 15 times, i.e. 1500% as great against mineral oil, 6 times or 600% as great against oleic acid, and up to 3 to 4 times or 300 to 400% as great against the extremely strongly penetrating: turpentine for instance, between about and about v as measured by TAPPI Standard T-45m-44.

Greatest improvements in both density and grease re sistance will, of course, result when my treatments areapplied to the lowergrades of greaseproof papers, i.e.. those which if processed to glassine, would have relatively low greaseproof characteristics and relatively high gas. permeability or porosity characteristics. Thus, my invention provides a means for upgrading such lower gradesv and bringing them into higher categories of usefulness.

hydrated cellulosic papers, for example, chemical or semichemical wood pulp papers, particularly coniferous wood pulp papers such as sulfite orsulfate pulp, hydrated so as Schopper-Riegler freeness-tester preferably papers made from pulps havingfreenesses bya-the'abovemethod between about 250 ml.- and about 150 1111." So-called greaseproof papers are J especially suita'ble for treatment according to the invention. The -so-calledgreaseproof papers are papers prepared-fromtunfilledsulfite and sul fate pulps which are highly hydratedbymechanicalactionalone (as distinct from: chemical treatment) in the presence of water, as bybeating, jordaning,.etc., and after formation, are machine calendered-.- They aIe'-d1Stll1-- guished from other-grades of unfilled sulfite papers Y such as. the so-calledwaxing papers-by the higher degree of hydration of the pulps from which they aremade, and are. thus adapted, I on-wet-supercalendering,-=toproduce densepapers having a high-degree of transparency. Thus, the so-called greaseprooff papers are-usually'prepared from unfilled .sulfite andsulfate :pulps having freeness characteristics, as theyreach-the paper machine, between ternatively, thetemulsion maybeapplied by a roll or brush rotating partially submerged in a trough of the emulsion to pick up. a layer of emulsionand transfer it either directly or. by intermediate means to the'paper, or

even by direct application at the nip OfILWO I'OIlS'thIOUgh which the paper passes. Usually: an excess of emulsion will be applied initially, and the excess aboveathatare quired to apply; the.desiredproportions of solids and moisture, will be removed.

The oxidized polyethylenewaxis preferably applie'd'so that as large a portion of the totalsolids as feasible will penetrate the pores of the paper, although a small-portion remaining. 0n=the surface ofthezpaper will do little harm.

The quantity of oxidized polyethylene waxaappliedais not unduly critical. Even small;quantitiesamayproduce significant enhancement; of ,the density and; grease :resistance characteristics of theresulting glassinepapers, :par-. ticularly those of proorer,grades..,.,In general,.iI find it desirable to deposit at least about 0.5% of.oxidizedpoly-. ethylene wax, based on, the weight'of the:paper, and sufficient to insure the, desiredincrease in density and.in the resistance to penetration. of gaseszand thewarious greases. In general, between-about0.5% andnabout 8% of the oxidized polyethylene-wax based onthezweightof. the

bone dry paper may; readily be applied, preferably. between about 2% and about 6%..

In any event, the emulsionwill be applied :so :as to deposit the requisite amountof oxidizedpolyethylene wax in the emulsion may be betweenqabout 10% and about.

40%,,preferably between-about-1;2% and about 20% to produce emulsionviscosities adapted to paper treating techniques andthe'depositionof adequate quantities of solids to effect the'desiredenhancement in density. and grease resistance.

The oxidized polyethylene wax suitable for use in the process of the invention may be .one having a molecular weight between about 1,000 and about 5,000. It may be prepared according to the process of copending application Serial No. 515,770, of Michael Erchak, In, or Serial No. 524,620, of Wilbur Chapman and John Cosby. Especially suitable are those obtained by oxidizing polyethylene/isopropanol telomer; waxes having average molecular weights betweenv about..1,000 and about 5,000 and containing between about 2% and about 7% oxygen, and a ratio of saponification'number to acid number of not more than about 1.5, preferably between about 1 and 1.2. These oxidized polyethylene waxes have superior hardness and toughness'characteristicsusually having penetration values-not more than about 0.5 mm. as measured by Standard ASTM method D-.-5-25 and toughness values of at least about 2.0 foot pounds per linear inch as measured by Standard ASTM method D-256-47T,

. and are readily emulsifiablein waterzsTI'he oxidized polyethylene wax emulsionsrmayzbe prepared .by: any suitable method, using any suitable emulsifying agentsyand the concentration ofn-thetoxidizedwwax.solids may. vary as required, to apply thepredetermined :amount of-oxidized wax to the papers; .A suitable oxidized polyethylene wax emulsion may be prepared, for -.example,:.by: melting the wax,:adding.a small. amountwof fatty acid .suchras oleic acid, 1111611,.Wiih .melt temperature at s ay,.-120-130 F.,' adding a small amount of an organic amine such as'morpholine. The resulting molten mixture may be added with rapid stirring tohot (99-- C.). water, at a steady rate to the top-of the vortexiormed rby; the. stirring, the wax I ,EXAMPLE'..

A roll-,of .greaseproof paper-.Sld imthes wide of a character suitable for thezpreparation of glassine paper, and having. physical. 2 characteristics :shown a in the table below, was divided into two equalsportionswhich were processedto glassine paper =by-wet calendering, in identical manner except. that the first portion was impregnated with water alone, thesecondwith a 15.6% aqueousemulsion of oxidized polyethylene wax, each to the extent of 30% of the papers'original weight.

The oxidized polyethylene wax was an-oxidized polyethylene/isopropanol telomer-wax containing'about- 3% oxygen and having an average molecular weight about 1500. It was emulsified-by melting 30 parts of the wax with 6 parts of morpholine, and adding 'the molten mixture with stirring to 138 partsof' 95-99 crwater-as described above. I

Each web of paper was= tub' sized with treating'liq'uid,

i.e. was immersed in andupassedthrough -the=treating'-" liquid located in a tray adjacentthesize pressof a conventional Mayer-coating-machine, the web travelling at a speed of 8 ft. per minute. It was passed through the nipof two-press=rollsadjusted to insure a' moisture con tent in the paper of about 25-30%? Both'webs were wound into rolls immediately after passing through 'the wet calenderingw The moist paper was 'then 'cut into shcets='9 "x' 5% and calendered on. a laboratorycalender consisting :of a

pair of steel rolls and an intermediatefilled paper roll, at a surface temperature of 155 F. and a pressure equivalent to 6,180 psi. at the nip. Each sheet was passed through the nip ten times to simulate the calendering operation in the production of commercial glassine paper.

The resulting calendered products were tested for gloss, brightness, opacity, porosity and grease resistance by the methods outlined below. Results of the, tests are given in Tables I and II which alsolist the values of the above characteristics in the raw greaseproo stock prior to treatment.

Gloss was measured by a Photovolt 75 degree gloss meter according to TAPPI standard T-480m-51.

Brightness was measured on a standard Photovolt unit in terms of blue light reflectance as compared to a magnesium oxide standard.

Opacity was determined on a Photovolt opacity meter in terms of comparative reflectance from white and black backings.

Porosity was determined on a Gurley densometer according to TAPPI standard T460m-49. Results are reported as the number of seconds required for 100 ml. of air to pass through one square inch of paper.

Grease resistance tests were made with turpentine according to TAPPI standard T-454m44 and with lard, Crisco (hydrogenated cotton-seed oil), cocoa butter, oleic acid and mineral oil (all containing a red dye) by a modification of the above TAPPI test in which the specimen was placed on a horizontal surface and backed by a piece of white coated paper. Then, 0.25 gram of grease was placed on aluminum foil. The foil with grease was inverted onto the specimen, and a weight placed on top of the foil and allowed to remain for seconds to create a uniformly smooth layer of the grease. Thereafter, a five gram portion of dry sand ,was placed on top of the foil to hold the specimen in firm contact with the coated paper. During the first two minutes of the test, the paper specimen was moved at 30 second intervals in order to observe whether or not spotting of the underlying coated paper had occurred. After the initial period more frequent additional observations were made. The results are reported as time in seconds elapsed to the appearance of the first red stain on the coated paper.

Table Physical characteristic of glassine paper made with oxidized polyethylene wax emulsion 6 proof paper, it may be applied in similar manner to th manufacture of other dense paper specialties such as onetime carbonizing paper, condenser tissue, etc.

While the above describes the preferred embodiments of the invention, it wil be understood that departures may be made therefrom within the scope of the specification and claims.

I claim:

'1. A process for increasing the density of a highly hydrated, chemical-pulp paper, which comprises incorporating into and onto the fibres thereof between about 0.5% and about 8% of an emulsifiable oxidized polyethylene wax having an oxygen content between about 2% and about 7% an average molecular weight between about 1,000 and about 5,000 and thereafter wet calendering the paper.

2. A process for increasing the density of a highly hydrated, chemical-pulp paper, which comprises applying thereto between about 20% and about 50% of its weight of an aqueous emulsion containing between about 10% and about 40% of an emulsifiable oxidized polyethylene wax having an oxygen content between about 2% and about 7% an average molecular weight between about 1,000 and about 5,000, and thereafter wet calendering the paper.

3. A process for producing a highly grease resistant glassine paper which comprises applying to greaseproof paper between about 20% and about of its Paper Characteristic Oxidized "Grease- Wet Ool- P.E. proof as endered Treated received and wet calendered Basis Weight e 25. 3 25. 3 26. 5 Caliper b 1. 50 1. 48 1. 40 Density 1. 078 1. 092 1. 210 Gloss:

Felt side-.. 30. 8 33.0 36. 6 Wire side 27. 1 32.0 30. 2 Brightness 62. 2 57. 5 46. 0 47.0 42. 3 44. 7 2, 316 7, 417 29, 860

50 5 40 250 '715 Cacao Butter e No spots e No spots N 0 spots Oleic acid 60 Mineral oil L-.. 152 6, 300

a 24 x 36-500. b Thousandths of an inch. T-454m-44. d Seconds for first spot to appear. e After 600 minutes.

weight of an aqueous emulsion containing between about 12% and about 20% ofan oxidized polyethylene wax having an oxygen content between about 2% and about 7% an average molecular weight between about 1,000 and about 5,000 and thereafter wet calendering the paper.

4. A process for producing a highly grease resistant glassine paper which comprises applying to greaseproof paper about 30% of its weight of a 12%20% aqueous emulsion of an oxidized polyethylene wax having an oxygen content between about 2% and about 7% an average molecular weight between about 1,000 and about 5,000 and thereafter wet calendering the paper.

5. As an article of manufacture a dense, highly hydrated chemical-pulp paper sheet, having incorporated therein between about 0.5% and about 8% of an emulsifiable oxidized polyethylene wax having an oxygen content between about 2% and about 7% an average molecular weight between about 1,000 and about 5,000.

6. A process for increasing the density of a highly hydrated, chemical-pulp paper, which comprises incorporating into and onto the fibres thereof, between about 0.5% and about 8% of an emulsifiable oxidized polyethylene wax having an average molecular weight between about 1,000 and about 5,000 and containing between about 2% and about 7% oxygen.

7. A process for increasing the density of a highly hydrated, chemical-pulp paper, which comprises incorporating into and onto the fibres thereof, between about 0.5% and about 8% of an emulsifiable oxidized polyethylene/ isopropanol telomer wax having an average molecular weight between 1,000 and about 5,000 containing between about 2% and about 7% oxygen and having hardness characteristics corresponding to penetration values of not more than about 0.5 mm. as measured by Standard ASTM method D-525, and toughness of values of at least about 2.0 foot pounds per linear inch as measured by Standard ASTM method D-25647T.

8. As an article of manufacture a glassine type paper comprising a highly hydrated chemical-pulp paper sheet, having incorporated therein between about 0.5% and about 8% of an emulsifiable-oxidized polyethylene/isopropanol telomer wax having an oxygen content between about 2% and about 7%, and an average molecular weight between about 1,000 and about 5,000, said sheet having a porosity value, as measured by the Gurley densometer, of about 30,000, and a resistance to turpen- UNITED' 1 STATES PATENTS Heinrich NOV. 4, 1952 Rill nbfg l Jfiil 16, 1953 Hunter Sep't. 1953 Schlatler Dec; 29, 1953 Nelson Apr. 6, 1954 10 "2,829,118

8 Constance Apr. 20, 1954 "I-ra'clit :4; Feb. 15, 1955 Erhak July 5, 1955 OFlyn'n .1 .'Mar. 20, 1956 Dec. 4, 'Ba'ikdoll 1 Dec. 25,1956 Dannels Apr. 9, 1957 Backlund May 7, 1957 Backlund May 7, 1957 Hanau Apr. 1, 1958 

1. A PROCESS FOR INCREASING THE DENSITY OF A HIGHLY HYDRATED, CHEMICAL-PULP PAPER, WHICH COMPRISES INCORPORATING INTO AND ONTO THE FIBRES THEREOF BETWEEN ABOUT 0.5% AND ABOUT 8% OF AN EMULSIFIABLE OXIDIZED POLYETHYLENE WAX HAVING AN OXYGEN CONTENT BETWEEN ABOUT 2% AND ABOUT 7% AN AVERAGE MOLECULAR WEIGHT BETWEEN ABOUT 1,000 AND ABOUT 5,000 AND THEREAFTER WET CALENDERING THE PAPER. 